Electron gun for cathode ray tube

ABSTRACT

The triode portion of an electron gun includes a cathode having an electron emitting material layer and a control electrode in which a through hole portion having a plurality of through holes for passing an electron beam is formed on a surface facing the electron emitting material layer so that the life span of the cathode can be prolonged.

BACKGROUND OF THE INVENTION

The present invention relates to an electron gun for a cathode ray tube,and more particularly, to an electron gun for a color cathode ray tubeprovided with an improved control electrode forming a triode portion.

Generally, as shown in FIG. 1, a cathode ray tube is basically composedof a panel 4 from which a shadow mask frame assembly 3 is spaced at apredetermined distance from a fluorescent film 2 formed on the innersurface of the panel, a funnel 5 sealingly attached to panel 4, and aneck potion of funnel 5 housing an electron gun 6 and having adeflection yoke 7 installed outside of the housing 5.

In the cathode ray tube constructed as above, an electron beam emittedfrom electron gun 6 is selectively deflected by deflection yoke 7,depending on the scanning position of fluorescent film 2 to thereby belanded on fluorescent film 2 resulting in forming a picture. In such acathode ray tube, an emission capability for emitting a thermal electronfrom electron gun 6 plays a critical role in the life span of thecathode ray tube. Accordingly, in order to prolong the life span of thecathode ray tube, a cathode exhibiting constant-intensity emissioncharacteristics should be employed.

FIG. 2 shows an example of such an electron gun for the color cathoderay tube.

The electron gun includes a triode portion 20, i.e., a source ofgenerating electron beam, a focus electrode 30 installed sequentiallyfrom triode portion 20 and having through holes to thereby form anauxiliary lens portion and a final acceleration electrode 40 which,together with focus electrode 30, forms a main lens portion.

In the electron gun constructed as above, a predetermined voltage issupplied to triode portion 20 and each electrode so that the electronbeam emitted from triode portion 20 passes through an electron lensformed between the electrodes, which is not shown in the drawings. Afterbeing converged and accelerated by the electron gun, the electron beampassing through the electron lens is landed on a fluorescent surface toexcite a fluorescent body and thus the picture is formed. Theperformance of the electron gun depends on the state (namely, the stateof a current density, the degree of halo effect and a diverging angle)of the electron beam emitted from the triode portion, i.e., the sourceof generating the electron beam. Accordingly, triode portion 20 is themost important part in the electron gun.

As shown in FIG. 3, a conventional triode portion 20 of such an electrongun includes a cathode 25 having a base metal 23 coupled to the end of asleeve 22 incorporating a heater 21. The surface of the base metal 23may be doped with an electron emitting material. A control electrode 26and a screen electrode 27 are each installed to be spaced from cathode25 at a predetermined distance and include through holes 26H and 27H forthe electron beam in a region aligned with in line with base metal 23.

In triode portion 20 constructed as above, with the emission of heat bysupplying a predetermined voltage to heater 21 of cathode 25, electronemitting material 24 is heated to thereby emit the thermal electron. Thethermal electron is preliminarily converged and accelerated by a cathodelens (not shown) formed by a through hole 26H for the electron beamformed in a control electrode 26 and a through hole 27H for the electronbeam formed in a screen electrode 27.

However, through hole 26H for electron beam of control electrode 26installed in front of cathode 25 forming the triode portion is formed tobe one hole. Therefore, the electric field forming the cathode lens orthat for forming main lens with final acceleration electrode 40receiving a high voltage is induced so as to extend to through hole 26Hfor the electron beam. Accordingly, the strongest electric field isformed on the central portion of cathode 25, namely, the central portionof electron emitting material layer 24, to concentrically emit thethermal electrons from the central portion of electron emitting materiallayer 24 to thereby be a main cause of the life span reduction ofcathode 25. Also, it is difficult to control the electron beam due tothe speed difference of the thermal electron between the central andouter portions of electron emitting material layer 24.

To solve such a problem, in the past, the central portion of the thermalelectron emitting material layer doped on the base metal is concavelyrecessed by concavely forming the surface of the base metal of thecathode to thereby reduce the effect of the permeated electric field.However, such a cathode cannot completely exclude the influence of theelectric field permeated from the through hole for the electron beamformed in the control electrode.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electron gun fora cathode ray tube for preventing the convergence of an electric fieldextending to a through hole for an electron beam of a control electrodeto the central portion of a cathode to prolong the life span of thecathode and control an electron beam easily.

To accomplish the above object, there is provided an electron gun for acathode ray tube including a triode provided with a cathode in which anelectron emitting material layer is formed and a control electrode inwhich a plurality of through holes for an electron beam are formed on asurface facing the electron emitting material layer of the cathode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail a preferred embodiment thereofwith reference to the attached drawings in which:

FIG. 1 is a cross sectional view of a general cathode ray tube;

FIG. 2 is an exploded cross sectional view for illustrating one exampleof a conventional electron gun for the cathode ray tube;

FIG. 3 is an exploded perspective view for illustrating a triode portionshown in FIG. 2;

FIG. 4 is an exploded cross sectional view of an electron gun for acathode ray tube according to the present invention;

FIG. 5 is a perspective view for illustrating a triode portion of theelectron gun according to the present invention; and

FIG. 6 is a cross sectional view for illustrating a visualized statethat an electric field extends to an electron beam passing portion of acontrol electrode shown in FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

An electron gun according to the present invention is mounted to theneck portion of a cathode ray tube to emit a thermal electron and oneembodiment is shown in FIG. 4.

The electron gun includes a triode portion 50, i.e., a source ofgenerating an electron beam, a focus electrode 60 which is installedcoaxially with triode portion 50 and to which a predetermined voltage issupplied and a final acceleration electrode 70. Here, triode portion 50generates an electron beam and controls the generation of the electronbeam. As shown in FIG. 5, triode portion 50 includes a cathode 55 and acontrol electrode 56 and a screen electrode 57 which are installedsequentially from cathode 55 and in which a through hole portion 80 forthe electron beam and a through hole 57H for the electron beam areformed.

Cathode 55 includes a heater 51, a sleeve 52 incorporating heater 51 anda base metal 54 installed to the end of sleeve 52 and having a electronemitting material layer 53 on the upper surface thereof.

Through hole portion 80 for the electron beam formed on a controlelectrode 56 of a portion facing electron emitting material layer 53 hasa plurality of uniformly distributed small through holes 81 for theelectron beam. Small through holes 81 for the electron beam may beformed to have varied diameters and the distribution thereof can bevaried as well.

In the electron gun for the cathode ray tube according to the presentinvention constructed as above, a predetermined voltage is supplied toheater 51 of cathode 55 forming triode portion 50 so that heater 51emits a heat to thereby heat electron emitting material layer 53. Alongwith the heating of electron emitting material layer 53, the thermalelectrons emitted from electron emitting material layer 53 pass througheach through hole 81 for the electron beam of through hole portion 80for the electron beam formed in control electrode 56. Since through holeportion 80 for the electron beam has a plurality of small through holes81 for the electron beam, it is possible to prevent the extension of theelectric field of the cathode lens formed between control electrode 56and screen electrode 57 and the extension of the electric field of finalacceleration electrode 70 and focus electrode 60 forming a main lensfrom focusing on a specific portion, namely, in the central portion ofelectron emitting material layer 53, as shown in FIG. 6. Accordingly, itis possible to make the speed of the thermal electron emitted from thecentral portion of electron emitting material layer 53 and a neighboringportion thereof uniform to thereby control the electron beam easily.Also, since the emission of the electron beam as in the conventionalmethod can be prevented from focusing on the central portion, it ispossible to prevent electron emitting material layer 53 located in thecentral portion from deteriorating in a comparatively short time andthus the life span according to the electron emission of electronemitting material layer 53 can be prolonged.

As described above, the electron gun for the cathode ray tube of thepresent invention having a plurality of through holes for the electronbeam forming the through hole portion for the electron beam formed inthe control electrode of the triode portion can be widely used not onlyin black-and-white and color cathode ray tubes, but also in a picturedisplay apparatus used in test equipment. The present invention is notlimited to the above embodiment and many alteration can be made by thoseof ordinary skill of the art within the scope of the technical ideas ofthe present invention written in the attached claims.

What is claimed is:
 1. A triode for an electron gun for a cathode raytube comprising:a cathode having an electron emitting material layer, acontrol electrode, and a screen electrode, the control electrodeincluding a plurality of through hole regions for an electron beam, eachthrough hole region having a plurality of through holes facing theelectron emitting material layer of the cathode, the screen electrodehaving a plurality of through holes corresponding to the plurality ofthrough hole regions, respectively.
 2. A triode according to claim 1,wherein the plurality of through holes for the electron beam areuniformly distributed in each through hole region.
 3. A triode accordingto claim 1, wherein the screen electrode includes a plurality of throughholes each through hole corresponding to a respective through holeregion in said control electrode and wherein a diameter of each of thethrough holes in the plurality of through hole regions is smaller than adiameter of the plurality of through holes in said screen electrode. 4.A triode for an electron gun comprising:a cathode having an electronemitting material layer; a control electrode including a through holeregion facing the electron emitting layer of said cathode, the throughhole region including a plurality of through holes; and a screenelectrode including through holes facing the through hole region of saidcontrol electrode.
 5. A triode according to claim 4 wherein each throughhole in the through hole region includes a diameter smaller than adiameter of the through holes of said screen electrode.